1. Field of the Invention
The present invention relates to patient monitoring. Although embodiments make specific reference to monitoring impedance and electrocardiogram signals with an adherent device, the system methods and device described herein may be applicable to many applications in which physiological monitoring is used, for example wireless physiological monitoring for extended periods.
Patients are often treated for diseases and/or conditions associated with a compromised status of the patient, for example a compromised physiologic status. In some instances, a patient may report symptoms that require diagnosis to determine the underlying cause. For example, a patient may report fainting or dizziness that requires diagnosis, in which long term monitoring of the patient can provide useful information as to the physiologic status of the patient. In some instances a patient may have suffered a heart attack and require care and/or monitoring after release from the hospital. One example of a device to provide long term monitoring of a patient is the Holter monitor, or ambulatory electrocardiography device, which may use electrodes attached to the skin to measure electrocardiogram signals from the patient.
In addition to measuring heart signals with electrocardiograms, known physiologic measurements include impedance measurements. For example, transthoracic impedance measurements can be used to measure hydration and respiration. Although transthoracic measurements can be useful, such measurements may use electrodes that may be somewhat uncomfortable and/or cumbersome for the patient to wear. In at least some instances, electrodes that are held against the skin of the patient can become detached and/or dehydrated, such that the electrodes must be replaced, thereby making long term monitoring more difficult.
Work in relation to embodiments of the present invention suggests that known methods and apparatus for long term monitoring of patients may be less than ideal. At least some of the known devices may not collect the right kinds of data to treat patients optimally. For example, although successful at detecting and storing electrocardiogram signals, devices such as the Holter monitor can be somewhat bulky and may not collect all of the kinds of data that would be ideal to diagnose and/or treat a patient for apnea and/or hypopnea. In at least some instances, devices that are worn by the patient may be somewhat uncomfortable, which may lead to patients not wearing the devices and not complying with direction from the health care provider, such that data collected may be less than ideal.
Although some current instrumentation for sleep studies, such as polysomnography, may be capable of determining an apnea hypopnea index (hereinafter “AHI”), work in relation to embodiments of the present invention suggests that current polysomnogram instrumentation may be les than ideal. To record physiological variable with a polysomnogram, a patient may sleep in a clinic while wearing skin electrodes that are tethered to a data acquisition system. Such use of skin electrodes tethered to a data acquisition system can be uncomfortable, relatively expensive, and may not duplicate normal sleep conditions, in at least some instances.
Although implantable devices may be used in some instances, many of the implantable devices can be invasive and/or costly, and may suffer at least some of the shortcomings of known wearable devices. In addition, implantation may require surgery that can subject an already frail patient to additional and undesirable physiologic stress.
Therefore, a need exists for improved patient monitoring. Ideally, such improved patient monitoring would avoid at least some of the short-comings of the present methods and devices.
2. Description of the Background Art
The following U.S. Patents and Publications may describe relevant background art: U.S. Pat. Nos. 4,121,573; 4,955,381; 4,981,139; 5,080,099; 5,353,793; 5,511,553; 5,544,661; 5,558,638; 5,724,025; 5,772,586; 5,862,802; 6,047,203; 6,117,077; 6,129,744; 6,225,901; 6,385,473; 6,416,471; 6,454,707; 6,494,829; 6,527,711; 6,527,729; 6,551,252; 6,595,927; 6,595,929; 6,605,038; 6,641,542; 6,645,153; 6,821,249; 6,980,851; 7,020,508; 7,041,062; 7,054,679; 7,153,262; 7,206,630; 7,297,119; 2003/0092975; 2005/0113703; 2005/0131288; 2005/0137464; 2005/0277841; 2005/0277842; 2006/0010090; 2006/0089679; 2006/122474; 2006/0155183; 2006/0173257; 2006/0195144; 2006/0224051; 2006/0224072; 2006/0264730; 2006/0173269; 2006/0161205; 2007/0021678; 2006/0031102; 2007/0038038; 2007/0073132; 2007/0123756; 2007/0129643; 2007/0150008; and 2007/0255531.